Fuse construction



June 29, 1943.

w. c. RUDD 2,323,006

FUSE CONSTRUCTION Original Filed Nov. 28, 1941 TERMINAL BLOCKS HEA TIER as/5L: ELEMENT 8A TURA TING INVENTOR.

MLLA CE C E000.

ATTORNEYS TRA Ms'Fo RMER Patented June 29, 1943 FUSE CONSTRUCTION Wallace 0. Rudd, Yonkers, N. Y., assignor to- Consolidated Edison Company of.-New York, Inc., New York, N. Y., a corporation of New York Original application November 28, 1941, Serial No. 420,773. Divided and this application Au-- gust 15, 1942, Serial No. 454,893

3 Claims. (c1.2o0--12s) This invention relates to fuse constructions, this application comprising a division of my copending application Serial No. 420,773, filed November 28, 1941, and now Patent No. 2,303,581, December 1, 1942.

r In power transmitting and distributing systems and networks, situations often arise wherein it would be desirable to provide a fuse or fuse arrangement designed to have a current timeblowing characteristic of one type when the power flow is in one direction through the fuse and of another type when the power flow is reversed, or when the current through the fuse is abnormally out of phase with the network or system potential. Such a difference in blowing characteristics would give the fuse a directional property which would be of value in cases, for example, where it is desirable to permit relatively large values of power to flow from one electrical system or device to another, and where it is also desired to prevent or limit to a lower rate, the flow of power in the reverse direction, or to limit the phase angle.

The invention of said divisional application provides circuit arrangements affording a solution for the above indicated problem. The fuse constructions comprising the invention of the present application will be described merely by way of illustrative example in conjunction with a preferred form of said circuit arrangements to thereby indicate one manner in which the present invention and its various advantages may be effectively utilized. According to the present invention a fusible structure is provided, in which the fusible element is associated with, and preferably substantially encioses, an electrical heating element which will become heated to a temperature sufiicient to melt the fuse and interrupt the circuit upon occurrence of abnormal conditions in the circuit, as for example upon occurrence of reverse power flow in case the fuse is used in conjunction with the invention of said divisional application. In that case the heating element may derive its heating current through connections across the power mains, which connections embody a source of potential which will normally substantially oppose the line potential, so that normally little or no heating current will flow; such normally opposing source of potential being so constructed and arranged that upon a reverse flow of power or when the fuse current becomes abnormally out of phase with the normal system or network potential, then the line potential as applied to the heating element will no longer be opposed but will cooperate with the other potential. Thus, a heating current will be permitted to flow, sufficient to cause blowing of the fuse.

The normally opposing source of potential may, for example, comprise a. suitable translating device such as a standard current type saturating transformer, the primary of which is in series with one of the power mains and the secondary of which is in serieswith the heater connections across'two of the power mains. This transformer may be so designed thatits secondary will provide a potential which isnormally' of about the-same magnitude as, but in opposition'to, the line potential but when the flow of power is reversed or the-fuse current becomes abnormally out of phase with the network potential, then the transformer secondary potential cooperates'with the line potential to cause the necessary current to flow through the heating element for blowing the fuse. g

If desired, the resistance ofthe heating element as well as the transformer secondary may be made adjustable whereby sufiicient heating current will flow whenever the phase angle between the line potential and fuse current exceeds a predetermined value, which may or may not necessarily be so great as to correspond to what may be called a reverse flow of power. Such adjustments may also be used to vary the timeblowing characteristic of the fuse as desired.

Various further and more specific objects; features, advantages and uses of the invention will appear from the description given below taken with the accompanying drawing illustrating by way of example certain preferred forms of the invention.

In the drawing,

Fig. 1 is a perspective view illustrating the construction of one simple form of the invention;'

Fig. 2 is a circuit diagram for the arrangement of Fig. l; and

Fig. 3 is a sectional view of a modified form of fuse element adapted for use in connection with the invention.

Referring now to the figures in further detail, a pair of power mains or busses are indicated at 10, H, the potential across which is represented byEL. These busses as shown in Fig. 2 may serve to connect a system A to a system B" of a distributing network in which power is-normally intended to flow from system A to system- B. A fuse construction l2 may for example be connected in series with bus II. This fuse is associated with, and for reasons hereinafter explained, preferably substantially encloses, an electrical resistance heating element l3. As shown in Fig. 2, one terminal of theresistance l3 may be connected to-one terminal of the secondary of a saturating transformer I4, the other secondary terminal being connected by connection l5-tothe bus or power main ll. Small fuses as at I 6 and I1 may be connected respectively in series with the terminals of resistance: l3 so as to interrupt the current to this 1 resistancein the event the resistance should be short-circuited upon blowing of the main fuse I 2. The other terminal of fuse H as shown may be connected to power main or bus l0, whereby the resistance l3, in series with the transformer secondary, is connected across the line.

The transformer I4 which may be a suitable known standard current type, is constructed for example with a core member l8 encircling a power main, so that the primary has but a part of one turn which comprises the power main or bus itself. The construction of this transformer, the parts of which need include only the core I8 and the secondary I9, may be like or similar to that of an ordinary current type transformer as used in connection with watt meters. transformer is preferably so designed and connected that its secondary will provide a potential E'r substantially equal in magnitude but opposed, with the connections as shown and described, to the normal line of system network potential EL. Thus, when power is normally flowing from system A to system B the potential E'r as applied to resistance [3 may be largely or wholly neutralized by the potential E1. as also applied to resistance l3, whereby little or no heating current will flow through the resistance. The fuse construction l2 may be so designed as to then blow only when the normal flow of power from system A to system B" is exceeded by a predetermined amount. direction of the flow of power reverses, and is from system B to system A through busses l0 and II, then the potential ET will also be reversed, with the result that the line potential and the transformer secondary potential as applied to resistance l3 will be added together, or at least cooperate to a suflicient extent to cause enough heating current to flow through resistance l3 to result in blowing the main fuse l2, when a predetermined rate of reverse power flow is exceeded, even though such reverse flow of power may be considerably less than what would normally blow the fuse if the heating element were not present, And as hereinafter explained in further detail, the heating element and transformer may be so designed as to cause the main fuse to blow when the current value exceeds a predetermined limit with the phase angle exceeding a predetermined value in either direction,

which angle may or may not necessarily be so great as to represent what would be termed an actual reverse flow of power.

It is advantageous to use a transformer of the so-called saturating type, so that regardless of variations in the amount of current through the power mains within practical limits, the secondary potential ET will remain substantially constant or near enough to a constant value to normally oppose the greater current which would otherwise flow through resistance l3. However, under conditions of no load, the potential E'r will of course become zero, or may become nearly zero under conditions of very light load. Under these circumstances, the line voltage less the voltage drop through the transformer secondary will be applied to the heating resistance l3 and cause partial heating. Yet, under these conditions, there will be little or no heating current through the fuse element l2 itself. Hence, the partial heating of the fuse by resistance I3 at these times is unimportant and will not cause blowing of the fuse.

A preferred form of fuse construction as shown in Fig. 1 may include a tubular fusible element 20 having a cylindrical cavity 2| for enclosing a The- However, when the part of the heating suitable known form of cartridge type heating element comprising the resistance l3. It is particularly advantageous to have the fusible ele-- ment surround and enclose or substantially enclose the heating element I3 so as to insure that all, or substantially all, of the heat generated in this resistance will be required to pass into the fusible element and thus be economically used for its intended purposes. This will not only minimize the amount of power required to operate the arrangement but also makes it possible to use an inexpensive and small saturating transformer. Furthermore, arrangements of this type will often have to be located in vaults or other enclosed spaces where the temperature is already high, thus making it important that heat radiation from resistance 13 be used economically and kept as low as possible.

Th fusible element 20 may be formed with integral enlarged hollow cylindrical end portions 23, 23 adapted to be received in suitable complernentary cavities as at 26 formed in supporting blocks 24 and 25, which in turn may be clamped together with the fuse end portions clamped therebetween, as by bolts 21.

With fuse arrangements as above described, it has been found in practice for example, that float currents of say 3,000 amperes with the forward power flow, and 1,500 amperes with the reverse flow are possible, and currents of the same ratio in the cas of fuses of either larger or smaller capacity,

The modified form of construction for the fuse and heater element as shown in Fig. 3 may be similar to that above described in connection with Fig. 1, except in this case the resistance element I3 is shown as a suitable known form of silicon carbide resistance heater, the ends of which are retained in suitable metal connecting clip assemblies as at 32, 33, which assemblies may be spaced by mica as at 34 from the walls of the fusible element 20'. The heater, clip assemblies and lead wires therefor may be secured within the fusible element 20' by a suitable known form of ceramic cement as at 35.

While the invention has been described in detail with respect to particular preferred examples, it will be understood by those skilled in the art after understanding the invention, that various changes and further modifications may be made without departing from the spirit and scope of the invention, and it is intended therefore in the appended claims to cover all such changes and modifications.

What is claimed as new and desired to be secured by Letters Patent is:

1. A fuse construction comprising in combination, an electrical resistance heating element, a fusible element substantially enclosing said heating element, means within said fusible element for normally effectively insulating said heating element against short-circuiting by the fusible element, and electrical connecting means extend ing from said heating element to the exterior of said fusibl element.

2. A fuse construction comprising in combination, a silicon carbide type electrical resistance heating element, and a fusible element within which said heating element is contained.

3. A fuse construction comprising in combination, an electrical heating element, a body of insulating ceramic cement surrounding same, and a fusible element within which said heating element and insulation are contained.

WALLACE C. RUDD. 

